Mao was on occasion swam across the Changjiang (or Yangtze River), especially in spring and summer. He also liked to swim across the Xiang River in his home province of Hunan. Every now and then his conversations were recorded, such as this one:
People say that the Changjiang is very big. In fact, something that is big is not formidable. You didn’t allow me to swim across, but now I have done it, haven’t I? Isn’t United States imperialism very big? But we stood up to it and so what? Therefore, some big things in the world are in fact not that formidable. (The Writings of Mao Zedong, vol 2, p. 676)
Not bad for a heavy smoker in his 60s.